1. Field of the Invention
The present invention relates to the manufacture of mineral fiber products, and in particular insulating products, in the form of felts or sheets of fibers. The manufacturing process employed includes the deposition on the fibers, by spraying or some other means, of a size based on phenoplasts or aminoplasts for bonding the fibers.
The present invention relates to a new condensation product or resin which is to enter into a sizing composition of the type described above, a process for the preparation of said product and a sizing composition containing said product.
2. Description of the Prior Art
The term "resin" as used in the context of the present invention means the product resulting from the condensation of reactive starting materials in the presence of a catalyst before any curing takes place in an oven.
The properties desired of sizing compositions depend to a large extent on the characteristics of the basic resin. A good sizing composition should above all be easily sprayed and capable of covering and bonding the fibers, and at the same time it should cause little pollution.
For this purpose, the basic resin should have good long term stability and a high degree of dilutability with water. Since the concept of dilutability is particularly important, it will be defined for the purposes of the present invention as follows: The water dilutability of a resin solution is the volume of de-ionized water which can be added at a given temperature to one unit volume of this solution without producing any permanent perturbation.
It is also necessary that the basic resin should be as free as possible from any uncoverted starting materials. The risk of atmospheric pollution is in fact mainly due to the presence of volatile monomers. These consist, for example, of the starting materials required for producing the resin, e.g. formaldehyde and phenol, which have been left uncoverted by the reaction or regenerated in the course of sizing of the fibres or subsequently.
In order, therefore, that the sizes obtained may be as free as possible from substances causing pollution, in particular free phenol and free formaldehyde, the basic resin should contain as little residues of starting material as possible while preserving its useful qualities.
In the past, the first resins proposed were obtained from phenol and formaldehyde in a molar ratio of F/P below 2.5, urea then being introduced only together with the other sizing additives after formation and storage of the resin in order to bind the free formaldehyde. Because of the low molar ratio of formaldehyde to phenol (F/P), it is not possible to obtain a free phenol content below 1.5% of the total weight of the resin solution, and the free formaldehyde content also amounts to at least 6%. Moreover, even the introduction of a large quantity of urea into the size in order to reduce this fre formaldehyde content does not enable the formaldehyde content to be controlled.
Various methods aimed at reducing the volatile free monomer content present in a sizing composition based on a phenoplast resin have been proposed. The principle of these methods is based on the idea of increasing the initial molar ratio of formaldehyde to phenol (F/P) in order to lower the uncombined and consequently free phenol content and at the same time bind the free formaldehyde present in excess by means of nitrogen compounds, in particular urea.
Various formulations of basic resins obtained from a molar ratio of formaldehyde to phenol in the range of from 2.7 to 4.2 in the presence of a basic catalyst have been envisaged. For example in U.S. Pat. No. 3,616,179, a condensation product of phenol, formaldehyde and urea has been proposed. The product obtained has a satisfactory capacity for dilution but, because of method of preparation employed, it is not possible to achieve a very low uncombined free phenol content while preserving the satisfactory capacity for dilution. The urea is introduced into the reactor where the reaction of phenol with formaldehyde takes place at a temperature suitable for this reaction, which is of the order of 70.degree. C. In order to avoid excessively rapid polymerization, which would entail the risk of problems of premature gelling which would prevent spraying of the sizes, the reaction of phenol with formaldehyde is blocked before most of the phenol has reacted.
In another technique as disclosed in U.S. Pat. Nos. 3,684,467 and 4,014,726, proposals have been advanced to prepare a condensation product of phenol, formaldehyde, dextrine or dicyandiamide and urea. To obtain this product, a first type of formaldehyde binding agent (dextrine or dicyandiamide) is introduced and reacted at a temperature corresponding to the reaction temperature of phenol and formaldehyde, and the urea is introduced and reacts as soon as cooling of the reaction medium has started.
Apart from the disadvantages already mentioned above regarding the incomplete conversion of phenol, this solution requires the presence of two formaldehyde binding agents. In addition, the temperature cycles are very long and require a length of time corresponding to more than one shift.
None of the solutions proposed in the prior art have ever provided a resin containing only a small proportion of free phenol and free formaldehyde in order to limit the problems of pollution, while preserving the characteristic properties of a resin suitable for entering into a sizing composition and in particular a high capacity for dilution and high stability. A need therefore continues to exist for a sizing composition which achieves these objectives.